Radio-frequency variable inductance



June 21, 1955 w. PERELSTRUS 2,711,518

RADIO-FREQUENCY VARIABLE INDUCTANCE Filed Aug. 10, 1951 2 Sheets-Sheet l M i .w @k on m ow 3 w v n N M \h n mm M 6 P am m+ m NW .N 7 low ww W June 1955 w. PERELSTRUS RADIO-FREQUENCY VARIABLE INDUCTANCE 2 Sheets-Sheet 2 Filed Aug. 10, 1951 3 nventor Wf/fiam Pere/sfrus (I ttorneg United States Patent Engineering, Inc., Pennsylvania Pa., assignor to Jordan Philadeiphia, Pa., a corporation of Appiication August 10, 1951, Serial No. 241,295 10 Claims. (Cl. 336-149) This invention relates to tuned portable transceivers and more particularly to variable radio-frequency gangable inductances therefor.

Considerable progress has been made in enhancing the portability of radio transceivers and similar equipment by reducing the weight and size of components and by the use of printed circuitry in the construction of conductors, resistors, capacitances and inductances.

it is a principal purpose of this invention to still further reduce physical dimensions and improve portability of such apparatus and to simplify tuning control.

A further purpose of the invention is to provide a simplified inductance coupling of the several radio-frequency stages and to tune them simultaneously by rotation of a single control over less than a complete revolution.

Still another object of the invention is to provide a variable wafer inductance to supplant the conventional multiturn adjustable core and slug inductances presently in use.

With these and other objects in view which will become apparent from the ensuing description and claims, the following sets forth the details of construction and combination of parts of a specific embodiment of my invention, which i illustrate as an example, and which will best be understood when read in conjunction with the accompanying drawing, in which:

Fig. l is a diagram of connections of the front end of an FM broadcast receiver.

Fig. 2 is a side elevational view, partly in section, of an assembly of principal components for the circuit of Fig. 1.

Fig. 3 is a rear end view of the device of Fig. 2.

Fig. 4 is a sectional view on the line 4-4 of Fig. 2.

Fig. 5 is a rear elevation of my variable inductance.

Fig. 6 is a side elevational view, partly in section, of the inductance of Fig. 5.

Fig. 7 is a rear elevational view, similar to that of Fig. 5, of a modification of my variable inductance.

Fig. 8 is a front elevation of the device of Fig. 7.

Referring now to the drawing, I have shown in Fig. 1 a circuit diagram of the front end of a frequency-modulated broadcast receiver comprising an antenna coupler, radio-frequency stages, mixer and local oscillator, for 4754 megacycle tuning range, with output to a 4.2- megacycle intermediate-frequency amplifier. The diagram of connections or hook-up shown forms no part of the invention, is substantially known and therefore will not be described further than is necessary to assist understanding of the components subsequently to be described. It consists of valves V1, V2, etc., resistances R1, R2, etc., capacitances C1, C2, etc., inductances L1, L2, etc., crystal K and conductors connecting these components. The subsequent description will be directed principally to the inductances, and more particularly to the construction and assembly of the variable inductances.

Fig. 2 illustrates a method of mounting the variable inductances L2, L4, L6 and L10 for ganged operation in Zfiilfiid Patented June 21, 1955 simultaneously tuning the several stages of the circuit of Fig. 1 from the antenna A to the mixer valve V3. The assembly 20 comprises individual vertically disposed stage mounting plates 21, 22, 23 and 24 of suitable insulating material fixed in spaced parallel relation by through tie rods 25 and 26, at top and bottom respectively, having sleeve spacers 27 between the respective plates and nuts 28 threaded on the ends. Attached to each of plates 21, 22, 23 and 24 is a valve socket 29 for respectively mounting valves V1, V2, V3 and V4.

A rotatable shaft 30 extends through the assembly 29 transversely of the mounting plates which are respectively suitably drilled to constitute the shaft bearings, the shaft 3%) being provided with a nut 31 threadedly attached to the rear end 32.

The variable inductances L2, L4, Ls, and L10 are wafers of disk shape bored axially for attachment to the shaft 39 by means of integral coaxial collars 35 provided with radial set screws 36. These wafer inductances are so disposed along the shaft 3i with tie collars 35 directed toward the front or right as viewed in Fig. 2, that the rearward faces of the wafers are adjacent the respective forward faces of the plates 21, 22, 23 and 24. The front end of the shaft 30 is provided with a knob 33 to facilitate manual tuning.

The wafer inductance L2, which is typical of the gangabie variable inductances and is illustrated in more detail in Fig. 5, is essentially a disk 37 of suitable material having adequate mechanical and dielectric properties, on the rearward face of which is printed a fiat spiral Winding 33. The winding 38 terminates outwardly in a substantially circular outer contact ring 39 and inwardly in a substantially circular inner contact ring 4%, the rings 39 and 40 being relatively much wider than the conductor of the spiral winding The contact rings 39 and 49 and winding 38 are applied or attached to the disk 37 by any of the wellknown methods of printed circuitry such as, cementing metal sheet or foil to the base, printing the desired winding on the metal with an inhibitor ink and etching away all the undesired metal; cementing to the base a punched-out or otherwise preformed Winding; spraying conducting metal or material into preformed grooves in the base; or by applying conductive silver preparations in the desired configuration, curing and plating with metal.

The outer ring 39 begins at a point 41 and terminates short of a complete circle at the point 52 where it connects with the outer end of the inwardly counterclockwise spiral winding 38 whose inward end is connected by a radially inward extension 4-3 to one end 44 of the incomplete-circle inner ring i t) such that the continuation of the circuit path from the spiral 38 around the ring 40 is clockwise or reversed from that of the spiral, to terminate at the other end 45 of the contact ring 49. The end M of contact ring 39 is approximately in diametral alignment with the end 4-5 of contact ring iii to per iit unbroken respective engagement of these contact rings over nearly a complete turn of the disk 37 by a pair of fixed contact members 46 and 47 suitably disposed on diametrically opposite sides of the shaft 30. A pair of the contact members 46 and 47 is attached on the rearward surfaces of each of the plates 21, 22, 23 and 24, each contact member having provision for connection to the external circuit and passing through a suitable respective I aperture 48 in the plate to engage the respective contact ring 39 or 40 of the juxtaposed wafer inductance. Suitable stop pins Si) in the disk 37 or equivalent means may be suitably disposed to prevent the contact members overrunning the ends of the contact rings, or otherwise to limit the de ree of rotation.

For any angular position of the wafer inductances with respect to the associated contact members, it is apparent from Fig. 5 that the complete spiral winding 38 is always included between these contact members. With the outer contact member 46 at the end 42 of the ring 39 or at the extreme clockwise position of the water inductance with respect to the contact members, the inner contact member 47 will be at the end 44 of the ring 40, and the inductance between the contact members will be a minimum or substantially that of the spiral winding 38 alone. As the wafer inductance is rotated counterclockwise, proportionally increasing portions of the rings 39 and 49 will be included between the contact members until with contact member 46 at the end 41 of the ring 39, contact member 47 will be at the open end 45 of the ring 40. In this position the entire length of both rings will be included between the contact members and the inductance will be a maximum. The explanation of this is as follows: It will be observed that as the wafer inductance is rotated counterclockwise from the extreme clockwise or minimum inductance position and portions of the contact rings are included in the circuit, the current path is reversed in the inner ring 46) as compared with the outer ring 39 and the spiral winding 38, and the increased inductance introduced by including increasing arcs of the ring 39 would tend to be cancelled out or neutralized by the corresponding arcs of the ring to. the outer ring 39 has a much larger radius and is therefore proportionately longer than the ring 4% it will have a predominant effect on the inductance and the net efiect will be to increase the inductance as the wafer is rotated counterclockwise.

The antenna coupling fixed inductance L1, is a spiral winding 52 printed on the forward face of the rear plate 21 whereby it is inductively coupled to the adjacent rotatable Wafer inductance. The disposition of the winding 52 relative to the associated adjacent winding 38 is shown by the dotted lines in Fig. 2. The remaining inductances L3, L5, L7, L8 and L9 are fixed spiral inductances suitably printed and disposed on the plates 21, 22, 23 and 24 and illustrated in Pig. 3 by the inductance 54 on the rear face of the plate 23..

By appropriate dimensioning and arrangement of the inductances described and suitable selection of the remaining circuit components, the circuit of Fig. l is readily tunable within the selected range by manual rotation of the knob 33 within a single turn.

It is obvious that the circuit of Fig. 1 and assembly of Fig. 2 can be extended to include the tuned stages of a transmitter which may be associated with the receiver components on a single chassis to form a transceiver tunable with a single shaft.

Although i have illustrated my wafer inductances in a circuit tunable in the 47-64 megacycle range, it should be understood that they are equally well adapted for use in tuning circuits tunable in any portion of the radiofrequency spectrum.

If it is desired to increase the inductance of the wafer inductance illustrated in Pig. 5, this may readily be accomplished as illustrated in Figs. 7 and 8 by printing on the reverse face of the disk 37 (similar to the disk 37 of Fig. 5), i. e. the front face 6% opposite the rearward face viewed directly in Fig. 7, a second spiral winding 33 similar to the winding 33 on the rearward face, but spiralling inward in the same angular direction as the Winding 38 when viewed from an external point. The inner end of the spiral 32- of this modification, instead of being con-. nected to the ring 4% as in Pig. 5, is connected to the outer end 61 of the spiral 33 on the front face 69 of the disk 37 by a suitable conductor 62 passing through an aperture 63 in the disk adjacent the inner end of spiral 33 and bridging the turns of the front face spiral 38'. Where it bridges the turns of the spiral 38', the conductor 62 is suitably insulated therefrom, for example by being spaced forwardly thereof. An extension 43' connected to the end 44 of the inner ring 40 is brought through a suitable second aperture 6-: in the disk 3'7 and connected to the inner end 66 of the spiral 38' on the face 60. The

However, since front face spiral may alternately spiral inwardly in the opposite angular direction, in which case the inner ends of the spirals would be interconnected by means of a conductor passing through a suitable hole in the disk such as the aperture 63 and a conductor connected to the outer end of the reverse face spiral would be bridged radially inward over the spiral turns then pass through a suitable hole in the disk such as the aperture 64 and be connected to the extension 43.

Although the invention has been described in considerable detail, such description is intended as illustrative rather than limiting, as other embodiments will be evident to those skilled in the art, as Well as obvious modifications in construction and arrangement of parts, without departing from the spirit of my invention.

1 claim:

1. In an electric circuit, a variable inductance comprising a Wafer of electric insulating material, a spiral conductor fixed to one face thereof, an arcuate noncontinuous outer contact ring fixed to said face and having one end connected to the outer end of said spiral, an arcuate non-continuous inner contact ring of smaller radius than said outer contact ring fixed to said face and having one end connected to the inner end of said spiral, said contact rings being concentric with said spiral and the current path of one ring being in the same angular direction as the spiral and the current path of the other ring being reverse to the angular direction of the spiral, means to rotate said wafer coaxially of said spiral, and fixed contacts continuously engageable with the respective rings as said wafer is rotated.

2. The invention set forth in claim 1 characterized in that the current path of said outer contact ring is in the same angular direction as the spiral.

3. The invention set forth in claim 1 characterized in that said spiral conductor and contact rings are printed metallic conductors.

4. The invention set forth in claim 1 characterized in that each of said contact rings is a circle having an insulating gap therein.

5. The invention set forth in claim 1 characterized in that said contacts and the connections of said contact rings to said spiral are in approximately diametral alignment on either side of the spiral axis.

6. The invention set forth in claim 1 characterized in including means to limit the rotational movement of said water with respect to said contacts.

7. In an electric circuit, a plurality of variable inductances each comprising a Wafer of electric insulating material, a spiral conductor fixed to one face thereof, two arcuate non-continuous contact rings fixed to said face and connected respectively to the inner and outer ends of said spiral concentric therewith and with the current path in opposite directions in said rings and the ring connected to the inner end of said spiral being of smaller radius than the ring connected to the outer end thereof, a shaft mounted for rotation, each of said variable inductances being disposed along and fixed to said shaft coaxially of the respective spirals, and a pair of fixed contacts associated with each inductance constructed and arranged continuously to engage the respective rings thereof as said shaft is rotated.

8. The invention set forth in claim 7 characterized in having a fixed spiral inductance associated in inductive relation with one of said variable inductances and and the ring connected to the inner end of said spiral being of smaller radius than the ring connected to the outer end thereof, a shaft mounted for rotation, each of said variable inductances being disposed along and fixed to said shaft coaxially of the respective spirals, and a pair of fixed contacts associated with each inductance constructed and arranged continuously to engage the respective rings thereof as said shaft is rotated, said inductances being severally appropriately dimensioned and arranged to accomplish tuning over the range desired within a single turn of said shaft.

10. In an electric circuit, a variable inductance comprising a Wafer of electric insulating material, a spiral conductor fixed to one face thereof, an arcuate noncontinuous outer contact ring fixed to said face and having one end connected to the outer end of said spiral, an inner arcuate non-continuous contact ring of smaller radius than said outer contact ring fixed to said face, a

second spiral conductor fixed to the opposite face of said wafer and having one of its ends connected to the inner end of said first-mentioned spiral and its other end connected to said inner contact ring, said contact rings and said spirals being concentric and the current path in both spirals and one ring being in the same angular direction and reverse to the current path in the other ring, means to rotate said wafer coaXially of said spirals, and fixed contacts continuously engageable with the respective rings as said wafer is rotated.

References Cited in the file of this patent UNITED STATES PATENTS 1,488,310 Birch-Field Mar. 25, 1924 2,503,582 Ginsburg Apr. 11, 1950 2,543,560 Thias Feb. 27, 1951 

